The present disclosure relates to metal pistons used in internal combustion engines fueled by gasoline, diesel, alcohol or any other combustible fuel. Internal combustion engine pistons are usually composed of two elements; a skirt and crown. The crown may have a plurality of circumferentially extending lands spaced from a top of the land toward the piston skirt with a groove disposed between adjacent lands for receiving a piston ring. Therefore, pistons have a series of alternating lands and grooves fabricated into the crown of the piston. In some piston examples the skirt and crown are joined by a mechanical method, e.g. welding. Other examples cast or machine the pistons as a one piece skirt and crown.
In operation, a piston is received within a mating cylinder or liner of an internal combustion engine. A lubricant such as oil minimizes friction as the piston moves up and down within the cylinder, portions of the piston (e.g., the piston rings) coming into sliding contact with a cylinder wall surface.
In reality, however, during engine operation, pistons are subjected to lateral and rotational forces as they move up and down vertically within a cylinder, causing the pistons to move in an eccentric motion within the cylinder or liner of the internal combustion engine. The eccentric motion takes the piston out of the desired straight vertical path within the cylinder or liner. The off center piston alignment may cause portions of the skirt, piston rings and lands to scrape the lubricating oil off of the cylinder wall, respectively breaking through of the oil film forcing metal to metal contact.
It is known to have a land adjacent to an uppermost land, a so-called second land, and the skirt provide the vertical guidance for the piston in its mating cylinder during engine operation. In previous piston embodiments where there are multiple lands, the second land has a greater axial extent (e.g., is taller) than the other lands positioned below it (e.g. intermediate and bottom lands). Moreover, at most there is only a minimal oil film between the second land and the cylinder wall or liner during engine operation with limited lubrication and hence limited damping of the rocking motion of the reciprocating piston within the cylinder.
An approach to introduce a guidance land spaced away from the heat of combustion such as the bottom land has been developed to significantly dampen the kinetic forces that cause the eccentric and otherwise erratic piston movement within a mating cylinder during engine operation. Therefore, lubricant such as in the form of an oil film remains intact on the cylinder or liner wall. Metal to metal contact and wear, piston power loss through undesired frictional contact, and possible temperature spikes resulting from enhanced frictional contact are all reduced.
Reducing the lateral and rotational motion of the piston also reduces the noise generated by the phenomenon known as piston slap. Limiting unnecessary, detrimental movement and frictional contact of engine pistons also increases engine efficiency. The present disclosure combines several modifications to the piston crown and skirt, thereby resulting in greatly improved engine performance and efficiency.